Where is the leak?

Hey all, after patching a hole I found in my tank, it appears there's another leak somewhere as well. When the tank is around 1/2 full, there is no sign of a leak, but after filling it up for the first time since patching the tank, it appears there's another leak somewhere. What's strange is I see no signs of a leak on the upper half of the tank, but there is a fair amount of fuel on the underside plastic.

It only appears to happen when the vehicle is or has been in motion. I didn't notice a leak while parked and running. Again, the only signs of the leak are on the underside of the tank where the vented plastic is attached to the tank. Any ideas?

Found it! There was a massive hole, roughly 1in in diameter, that had been siliconed over by some repair shop in the past (prior to my ownership). I found a metal fitting, jb welded it into place, and placed a screw in the hole of the fitting. (on the off chance that there was once a pressure tube there).